A medical imaging apparatus is an apparatus for acquiring an image of an inner structure of an object. A medical imaging apparatus noninvasively images and processes structural details, tissue, and the flow of a fluid in a patient's body to be examined and displays a result of the imaging and processing to a user. The user, for example, a doctor, may check the patient's health condition and may diagnose the patient's disease by using a medical image that is output by the medical imaging apparatus.
A computed tomography (CT) apparatus is a representative apparatus for imaging an object by emitting X-rays to a patient.
Since a CT apparatus that is a tomography apparatus among medical imaging apparatuses may provide a cross-sectional image of an object and may display an inner structure (e.g., organs such as kidneys and lungs) of the object without an overlap therebetween, unlike a general X-ray imaging apparatus, the CT apparatus is widely used to precisely diagnose a disease. Hereinafter, a medical image that is obtained by a tomography apparatus is referred to as a tomography image and a medical image that is obtained by a CT apparatus is referred to as a CT image.
In order to obtain a tomography image, tomography imaging is performed on an object by using a tomography apparatus to obtain raw data. A tomography image is reconstructed by using the obtained raw data. The raw data may be projection data that is obtained by projecting X-rays to the object or a sinogram that is a set of projection data.
For example, in order to obtain a tomography image, an operation of reconstructing an image has to be performed by using a sinogram that is obtained through tomography imaging. An operation of reconstructing the tomography image will now be explained with reference to FIGS. 1A and 1B.
FIGS. 1A and 1B are views for explaining CT imaging and reconstruction.
In detail, FIG. 1A is a view for explaining an operation performed by a CT apparatus to perform CT imaging by rotating about an object 25 and obtain raw data. FIG. 1B is a view for explaining a sinogram and a reconstructed CT image that are obtained by the CT imaging.
The CT apparatus generates X-rays, emits the X-rays to the object 25, and detects the X-rays that pass through the object 25 by using an X-ray detector (not shown). The X-ray detector generates raw data corresponding to the detected X-rays.
In detail, referring to FIG. 1A, an X-ray generator 20 that is included in the CT apparatus emits X-rays to the object 25. During CT imaging, the X-ray generator 20 rotates about the object 25 and acquires a plurality of pieces of raw data, e.g., first through third raw data 30, 31, and 32, corresponding to rotation angles by which the X-ray generator 20 rotates. In detail, the first raw data 30 is obtained by detecting X-rays that are applied to the object 20 from a position P1 and the second raw data 31 is obtained by detecting X-rays that are applied to the object 25 from a position P2. Also, the third raw data 32 is obtained by detecting X-rays that are applied to the object 25 from a position P3. Each of the first raw data 30, the second raw data 31, and the third raw data 32 may be projection data that is obtained by emitting X-rays to the object 25 from one view.
In order to obtain one cross-sectional CT image, the X-ray generator 20 has to perform CT imaging by rotating by at least 180°.
Referring to FIG. 1B, one sinogram 40 may be obtained by combining a plurality of pieces of projection data, e.g., the first through third raw data 30, 31, and 32 together, obtained by moving the X-ray generator 20 by predetermined angular sections, as described above with reference to FIG. 1A. The sinogram 40 is a sinogram obtained by the X-ray generator 20 that performs CT imaging by rotating by one cycle. The sinogram 40 corresponding to the rotation of one cycle may be used to generate one cross-sectional CT image. The rotation of one cycle may be equal to or greater than a half-turn or one turn according to a specification of a CT system.
A CT image 50 is reconstructed by performing filtered back-projection on the sinogram 40.
Various artifacts may occur in the reconstructed CT image 50. The various artifacts in the CT image 50 may reduce the quality of the CT image 50, thereby reducing the accuracy with which a user, e.g., a doctor, reads the CT image 50 and diagnoses a disease.
Accordingly, it is very important to reconstruct the CT image 50 with reduced artifacts.